The following represent the major defined objectives for the next five year award period. 1. Isolation and characterization of human thymocyte specific and peripheral T lymphocyte specific antigens detected by the current serologically defined nonhuman primate antisera described in the progress report. 2. In vivo and in vitro studies on the effect of the thymocyte specific and T lymphocyte specific primate antisera on human and simian lymphocyte functions. 3. Production and serological characterization of new simian antisera to human normal or malignant cell types which are predominately T or B in nature. 4. Expand the immunologic studies on experimentally produced T cell deficiencies in chimpanzees.